A conventional capper head for screwing a cap onto a mouth section of a container is shown in FIG. 4. A capper head 40 shown in FIG. 4 comprises a fixed gear 41 that is fixed to a frame not shown in the figure, a planetary gear 42 that is engaged with the fixed gear 41 and revolves, while rotating, around the fixed gear 41, a sliding bearing 44 that is engaged with an output shaft 43 of the planetary gear 42 to transfer the rotation of the planetary gear 42 and is supported to as to be free to slide in the axial direction relative to a rotary frame not shown in the figure, a torque limiter 45 that is linked to the output side of the sliding bearing 44 and restricts the upper limit of a tightening torque, and a chuck 46 that is linked to the output side of the torque limiter 45 and rotates a cap (not shown in the figure). The planetary gear 42 is engaged with the fixed gear 41 so that the planetary gear can move in the axial direction, and the planetary gear together with the sliding bearing 44, torque limiter 45, and chuck 46 can move up and down with respect to the rotary frame. For example, a magnetic limiter in which the torque is easy to manage and which does not practically generate dust can be used as the torque limiter 45. A cam follower 47 engaged with a lifting cam 48 that is attached to the fixing gear 41 is provided at the sliding bearing 44 to lower the chuck 46 as the cap is tightened.
With the capper head 40 of such configuration, when the planetary gear 42 is revolved around the fixed gear 41 with a drive means not shown in the figure, the sliding bearing 44 revolves together with the planetary gear 42, whereby the planetary gear 42, sliding bearing 44, torque limiter 45, and chuck 46 are lifted or lowered by the cam action of the lifting cam 48 and the cam follower 47 engaged therewith and the cap held by the chuck 46 is brought close to or withdrawn from the mouth section of a container. If screwing of the cap on the mouth section of the container is started, the planetary gear 42 rotates, while revolving together with the sliding bearing 44, torque limiter 45, and chuck 46, due to the engagement with the fixed gear 41, and the chuck 46 rotates the cap at a rate of this rotation of the planetary gear and screws the cap on the mouth section of the container. The rotation rate of the planetary gear 42 in this process is a constant rotation rate determined by the gear ratio of the planetary gear and fixed gear 41. The cap moves down around the mouth section correspondingly to the degree of tightening of the mouth section of the container and the pitch of the screwing thread, but a buffer section is provided in the upper part of the chuck 46 and absorbs the stroke difference caused by the rotation in excess of the number of turns necessary for tightening (about 3 turns). Because the chuck 46 descends correspondingly to the sinking degree of the cap when the cap is tightened, the capping operation is implemented without damaging the thread or incorrect tightening.
Another example of the conventional capper head is shown in FIG. 5. In a capper head 50 shown in FIG. 5, the elements common with the capper head 40 shown in FIG. 4 are assigned with the same symbols and the explanation thereof is omitted. The difference between the capper head 50 and the capper head 40 is in that a servo motor 51 is used instead of the planetary gear 42 and torque limiter 45. The rotation of the servo motor 51 is transmitted to the chuck 46 via a drive shaft 52 of the motor and the slide bearing 44 and a cap is tightened on the mouth section of the container. The servo motor 51, sliding bearing 44, and chuck 46 revolve integrally around a cam shaft axis 49 of the lifting cam 48 by a drive means not shown in the figure. Corresponding to this revolving action, all the components from the servo motor 51 to the chuck 46 via the sliding bearing 44 are brought close to or withdrawn from the mouth section of the container correspondingly to the tightening of the cap by the cam action of the cam follower 47 and lifting cam 48 provided at the external members of the sliding bearing 44.
In the capper head 40 shown in FIG. 4, the rotation rate of the planetary gear 42 is also the rotation rate of the chuck 46. Therefore, the rotation rate when the cap is tightened is also constant with respect to the revolution rate. Furthermore, the lifting stroke of the chuck 46 and the timing thereof depend on the cam shape of the lifting cam 48. Because the lowering degree of the chuck 46 is determined by the specifications of the container or cap, the cam shape of the lifting cam 48 has to be determined in advance. On the other hand, in the capper head 50 shown in FIG. 5, since the chuck 46 is rotated by the servo motor 51, the rotation rate of the chuck 46 can be randomly changed by the servo motor 51. Furthermore, the tightening torque can be randomly changed by the servo motor 51 in the course of operation.
In the above-described conventional capper heads, a lifting cam is used for lifting and lowering the chuck, but because the cam and cam follower are formed by processing wear-resistant materials, the processing cost is high and the production cost of the capper head or screwing apparatus is unavoidably increased. Furthermore, because the contact portions of the fixed gear and planetary gear and also the cam and cam follower are exposed, there is still space for improvement in terms of noise and dust generation. For the cam follower to slide inside a cam groove of the lifting cam, a grease is used as a lubricant in the contact zone, but even if a grease with a high viscosity is used, the spattering of grease during operation of the apparatus is difficult to prevent completely and the surrounding environment that has to be maintained in a clean state to handle the filled containers can be contaminated. Furthermore, when the specification including the thread pitch of the cap are changed, the lifting stroke and the timing thereof have to be changed, but the fixed gear or lifting cam have to be replaced to adapt to such a change.
A capper has been suggested in which container clamping mechanisms are provided in positions equidistantly spaced in the circumferential direction on a rotary table constituting a rotary body that is rotary driven by a motor, torque motors and cap clamping mechanisms that are rotary driven by the torque motors are attached in positioned immediately above each container clamping mechanism so that the torque motors and the cap clamping mechanisms can be lifted and lowered by a guide pole, the torque motors and cap clamping mechanisms are lifted and lowered integrally by the cam action with a cam mechanism fixed on the outside, and the drive shaft of the torque motor and the rotary shaft that rotates the cap clamping mechanism are key-joined, thereby enabling the transmission of torque motor rotation, while allowing the rotary shaft to be lifted or lowered. It was also suggested to control the drive torque produced by the torque motor according to the rotation position of the rotary body.
Patent Document 1: Japanese Patent Application Laid-open No. H10-324396 (Par. No. [0002]-[0003], [0007]; FIG. 1)